Albumin-constrained large-scale synthesis of renal clearable ferrous sulfide quantum dots for T1-Weighted MR imaging and phototheranostics of tumors

Ultrasmall-sized iron-based nanoparticles are showing increasing potentials to be alternatives as T1-weighted magnetic resonance imaging (MRI) contrast agents to the currently-used gadolinium-based compounds. However, their synthesis particularly in a large-scale and green fashion is still a big challenge. Herein, we report an albumin-constrained strategy to synthesize tiny and highly dispersible ferrous sulfide (termed FeS@BSA) quantum dots (QDs) at ambient conditions. FeS@BSA QDs exhibit ultrasmall size of ca. 3.0 nm with an ultralow magnetization, affording them an appealing longitudinal relaxivity for T1-weighted MRI. The design principle leverages on albumin-mediated biomimetic synthesis and spatial isolation of the protein interface prevents bulk aggregation of the particles. Albumin was found to play crucial roles in the synthesis process: a constrained-microenvironment reactor for particle growth, a water-soluble layer for colloidal stability and a carrier for multi-functionality. This synthetic strategy was found facile, green and particularly large-scalable to 10 L. Mice experiments show good T1-weighted MRI capability of FeS@BSA QDs, significantly lighting the whole body organs, blood vessels and tumors. And interestingly, these QDs can be further used to conduct phototheranostic of tumor benefited from their intense absorption at near-infrared region. In particular, they can be cleared via glomerular filtration into bladder after treatment. Given this approach is biomimetic, scalable and does not require any complicated chemical synthesis or modifications, the method demonstrated here will find great potentials for clinical translation in T1-weighted MRI of diseases and inspire other functional tiny nanoprobes for biomedical applications.